Discontinuation of mechanical ventilatory support represents a milestone in the progression to patient recovery in the Intensive Care Unit (ICU). Despite advances in mechanical ventilation and respiratory support, the science of determining if the patient is ready for extubation is still very imprecise. The goal of this article is to summarize key developments in this important clinical area.The following core competencies are addressed in this article: Medical knowledge and patient care.Republished with permission from: Stawicki SP. ICU Corner – Mechanical ventilation: Weaning and extubation. OPUS 12 Scientist 2007;1(2):13-16.

Discontinuation of mechanical ventilatory support represents a milestone in the progression to patient recovery in the Intensive Care Unit (ICU).[1],[2] Despite advances in mechanical ventilation and respiratory support, the science of determining if the patient is ready for extubation is still very imprecise. As a result, reported reintubation rates vary from 2% to as high as 25%, depending on the ICU population studied. The “optimal” reintubation rate is not known, but it has been postulated that a number between 5% and 10% indicates the “optimal” point, where relatively few extubations fail but the extubation protocols are not too “conservative” so as to unduly prevent appropriate extubations.[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13]

It has been estimated that over 40% of time spent on mechanical ventilation can be attributed to the weaning process itself. Delays in extubation have been associated with increased complication rates, including ventilator-associated pneumonia, airway trauma, increased hospital costs, and mortality. On the other hand, premature discontinuation of ventilatory support carries its own set of risks, including difficulty in re-establishing an airway, 8-fold higher odds ratio for nosocomial pneumonias, compromised gas exchange, and a 6–12-fold increased mortality risk.[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17],[18]

Liberation from mechanical ventilation is usually undertaken only after the underlying pathologic process that prompted the initiation of mechanical ventilation is improved or resolved. A focused, simple daily screening can identify patients who are potential candidates for extubation. These assessments are multi-faceted, and usually include the overall patient condition and hemodynamic stability, neurological and muscular status, the adequacy of gas exchange, among other variables. Daily screening can reduce the number of patients receiving mechanical ventilation for more than 21 days and has been associated with reduced in-hospital mortality. In approximately 10%–20% of mechanically ventilated patients, the weaning and extubation process can be very difficult and protracted– a phenomenon associated with the duration of mechanical ventilation of >21 days.

Because of the lack of sensitivity and specificity of the criteria listed above, significant research effort was devoted to determining clinically useful weaning parameters. There are two prominent reviews published in the late 1990's that generated a set of evidence-based clinical practice guidelines for managing the ventilator weaning process and extubation.[2],[17] Another meta-analysis evaluated a possible role of various clinical measurements as predictors for successful extubation.[19] Cumulatively, this work generated a list of several useful weaning and extubation parameters that are widely used today [Table 1].[20],[21],[22],[23],[24] Despite very high sensitivity (78%–100%), however, these parameters were plagued by low specificity (11%–36%).[14] Such low specificity in weaning parameters contributes to preventing of weaning and extubation in certain percentage of patients who are otherwise able to breathe independently.

Taking the theory a step further, the concept of spontaneous breathing trials (SBTs) was conceived. It may be that the best way to assess whether the patient is likely to tolerate extubation is to perform a trial of spontaneous ventilation. Studies have shown that between 60% and 80% of mechanically ventilated patients can be successfully extubated after passing a SBT. However, there is still a lot of controversy as to what is the best way to perform such SBTs, and many studies failed to demonstrate any significant differences between: (a) continuous positive airway pressure of 5 cm H2O versus T-piece for 1 h; (b) T-piece versus pressure support of 7 cm H2O; and (c) duration of SBT of 30 min versus 120 min. Given these mixed findings, it may be that the optimal way of interpreting SBT is to combine objective and subjective indicators of intolerance or failure of SBT [Table 2].[10],[12]

There is also evidence that the rapid shallow breathing index (RSBI) rate, or a measure of change of RSBI over time, may offer more predictive value than its RSBI predecessor. RSBI = respiratory rate/tidal volume. The RSBI rate is calculated by obtaining the difference between the initial RSBI and the final RSBI, and then dividing the result by the initial RSBI. The resulting number is then multiplied by 100. The mathematical formula is as follows: RSBI rate = ([RSBI2– RSBI1]/RSBI1) × 100. It was shown that RSBI rate of <20% was over 90% sensitive and 100% specific for predicting weaning success. It had a positive predictive value of 100% and a negative predictive value of over 81%.[21],[23]

Extubation

Once a determination has been made that a patient is likely to tolerate spontaneous, unassisted breathing, a decision has to be made with regards to actually discontinuing the artificial airway. One must keep in mind that failure to extubate can occur for reasons that are not directly related to weaning failure. Several important factors have to be carefully considered prior to extubation, including: (a) the presence of a patent airway; (b) patient ability to consistently protect the airway; (c) patient ability to clear secretions; (d) mental status compatible with maintenance of airway and secretion clearance; and (e) absence of any other reasons for potential postextubation failure (i.e., severe pain preventing adequate respiratory function, presence of apnea, poorly controlled seizures, risk of massive upper gastrointestinal bleeding, etc.). Key points pertaining to ventilator weaning and exbubation are provided in [Table 3].[1],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[20],[21],[22],[23],[24]

Table 3: Important points to remember when instituting ventilator weaning and attempting extubation

There are other important factors that have to be considered before extubation. While there is some evidence that successful extubation in comatose patients is possible, most intensivists agree that the patient should show at least some capability to interact with the environment and the health-care team prior to removal of the artificial airway. Patients with poor cough and moderate to severe secretions have been shown to have a high rate of failed extubation despite successfully completing SBT. Many of the patients who develop postextubation stridor can be treated with steroids, epinephrine, noninvasive ventilation, and potentially the use of helium-oxygen gas mixture (heliox). In general, <50% of patients with postextubation stridor require reintubation.

Another important consideration is the assessment of airway patency before extubation. Here, the absence of an audible air leak after endotracheal tube balloon deflation has been associated with an increased risk of postextubation stridor and subsequent need for reintubation. Another method of assessing the amount of “cuff leak” consists of dividing the expiratory volume by the inspiratory volume and multiplying the result by 100. The “cuff leak” value of <12%–16% has been shown to be predictive of extubation failure. Among patients on assist-control ventilation, a “cuff leak” of <110 mL between inspiratory and expiratory volumes has been shown to predict the development of postextubation stridor.

Historical note: Paracelsus (1493–1541) was an alchemist, physician, astrologer, and general occultist. Born Phillip von Hohenheim, he later took up the name Philippus Theophrastus Aureolus Bombastus von Hohenheim, and still later took the title Paracelsus, meaning “equal to or greater than Celsus,” a Roman encyclopedist from the first century known for his tract on medicine. At the age of 16 he started studying medicine at the University of Basel, later moving to Vienna. He obtained his doctorate degree from the University of Ferrara. Paracelsus, sometimes called the father of toxicology, wrote: “All things are poison and nothing is without poison, only the dose permits something not to be poisonous.”

Persistent Failure to Wean And/or Extubate

If failure to wean and/or extubate persists despite maximal and repeated efforts to achieve these endpoints, other steps may be required before successfully liberating the patient from mechanical ventilatory support. Some patients require prolonged and more gradual ventilatory weaning, which may be best facilitated by tracheostomy placement. In addition, data from observational studies show that up to 60% of ventilator-dependent patients who are discharged from the ICU can be successfully weaned when they are transferred to specialized units dedicated to ventilator weaning.[19],[20],[21],[22]

Summary

The process of weaning from mechanical ventilation and subsequent extubation constitutes a significant portion of the patient's ICU stay. Although many variables for successful outcomes have been identified, specific and reliably reproducible criteria have not been clearly established. Currently, combining objective and subjective endpoints represents the most reliable strategy for weaning from mechanical ventilation and subsequent extubation. Until more reliable weaning and extubation strategies emerge, it may be that weaning parameters are best individualized for each distinct clinical and patient scenario.

Acknowledgement

Justifications for re-publishing this scholarly content include: (a) The phasing out of the original publication after a formal merger of OPUS 12 Scientist with the International Journal of Academic Medicine and (b) Wider dissemination of the research outcome(s) and the associated scientific knowledge.